Volatile anaesthetic vaporising apparatus

ABSTRACT

A volatile anesthetic vaporizing apparatus including a rotary percentage control plate valve for controlling two divided inflowing gas streams, one stream being passed over liquid volatile anesthetic to form a vapor and the other bypassed through a duct controlled by a temperature responsive bypass valve, said plate valve also controlling the outflow of gas-vapor mixture, said bypass valve having a resistance characteristic which is inconstant.

United States Patent Wilfred Jones Riddlesden, Keighley;

[72] Inventors Ronald William cal-lei, Keighley, England [54] VOLATILEANAESTHETIC VAPORISING g g fi f f Fig and the other bypassed through aduct controlled by a temperature responsive bypass valve, sald platevalve also [52] US. Cl 128/188 cgntrolling the outflow of gas-vapormixture, aid bypass valve [51] Int. Cl A6lm 17/00 having a resistancecharacteristic which is inconstant,

m m u "3/ l2 l3 I4 V 1O 3 I 4 24 24 S I 22 f l l 5 I 7 I6 26 k I f 38 L9Q 26 21 3s 27 2 x E B34 Field 61 Search 128/188, 186,187,189,l92,196-197,203,210; 137/625.19, 625.29, 625.30, 625.31;

(Vap. Digest); /(lnquired);/

Primary Examiner-Richard A. Gaudet Assistant Examiner-J. B. MitchellAttorney-Pierce, Scheffler & Parker ABSTRACT: A volatile anestheticvaporizing apparatus including a rotary percentage control plate valvefor controlling two divided inflowing gas streams, one stream beingpassed over liquid volatile anesthetic to form a vapor PATENTEDAPR20197|3" 575 168 sum 2 BF 2 7 T IINVENTORS WiL'Y-red. ones 8 Ronald WilliamCarter 5 Pwei 2mm VOILA'lllllLlE ANAIESTIHETTC VAPORISHNG APPARATUS Thisinvention relates to apparatus capable of mixing the vapor of a volatileliquid anesthetic with a gaseous fluid, such as air, oxygen, or nitrousoxide, or a combination thereof, all three of which for convenience arehereinafter included in the term gas. The invention particularly relatesto the bypass type of anesthetic vaporizer where the' gas input to thevaporizer is divided into two streams which subsequently recombine. Onestream passes through a bypass circuit and the other stream passesthrough a vaporizing chamber where the gas flow becomes mixed with thevapor from a volatile anesthetic. Control valves are incorporated inthese two streams which may be adjustable to vary the finalconcentration of vapor obtained. 7

It is well known that the delivered concentration at different flowswith the same control settings may vary for many reasons, some of whichare as follows:

a. As the input flow to the vaporizer is increased, the flow through thevalve on the bypass stream increases at a different rate to the flowthrough the valve on the stream which passes through the vaporizationchamber.

b. The vapors of volatile anesthetic liquids are in general heavier thanthe carrier gases and this imposes an extra loading in the vaporizationstream.

c. The proportion of anesthetic agent in the gas flowing out of thevaporizing chamber may change as the input flow of gas to the chamberchanges due to such causes as cooling at the vaporizing surfaces, ordrying out of the wicks (if fitted) and changes in gas distribution inthe vaporizing chamber.

d. Resistance to flow due to ducting and other restrictions at positionsother than the control valves may upset the performance.

Difficulty (a) can be removed by making the valves so that the ratio ofthe flows of gas through the two streams previously referred to isindependent of flow. This can be done by having a valve system so thatfor each valve the first differential of pressure with reference to flow(the resistance characteristic) is independent of flow, i.e., the flowis streamline, or laminar, and

l;= constant This does not, however, help remove difficulties (b), (c)and (d) above and if streamline flow is used for both control valves thedelivered concentration will fall as the flow increases. This will beparticularly noticeable at high concentrations. According to the presentinvention we provide volatile anesthetic vaporizing apparatus of thebypass type wherein the gas input is divided into a first stream passingthrough a vaporizing chamber to become mixed with vapor from a volatileanesthetic, and a second stream, the two streams subsequentlyrecombining, in which the first stream is controlled by a percentagecontrol valve and the second stream is controlled by a bypass valveresponsive to the internal temperature of the vaporizer in such a waythat the pressure drop over the bypass valve increases as the totalvolume of gas flow through the vaporizer increases.

Thus the resistance characteristic, dp/dV, is not constant and thebypass valve does not give streamline flow, the degree of deviation fromstreamline characteristics being dependent on the internal temperatureof the vaporizer. When total gas flow into the vaporizer increases, theamount of gas flowing over the anesthetic increases and thus the rate ofevaporation increases and the temperature drops. This temperature dropacts to further restrict the bypass valve so that the pressure drop overthis increases and the gas flow through it decreases. Thus more gas isallowed to flow in to the vaporizing chamber than would otherwise be thecase, and the anesthetic concentration in the recombined stream can beheld substantially constant.

The percentage control valve may be made to have either streamline ornonstreamline characteristics. Desirably however the valve is designedto have different characteristics for different calibrated positions,because the relative importance of effects (b), (c) and (d) above aredifferent at different output concentrations. The degree of deviationfrom streamline flow characteristics for any particular setting willusually be somewhere between that of the bypass valve and that forstreamline flow, although the percentage control valve could be mademore nonstreamline than the bypass valve at certain settings if it werenecessary for any reason.

The invention will now be more particularly described with reference tothe accompanying drawings, in which:

FIG. 1 is a sectional elevation generally on line H of FIG. 3 but partlyin diagrammatic form for ease of description of the improved anestheticvaporizer;

- FIG. 2 is a plan view from below of a facing part of a control valve;

FIG. 3 is a plan view from above of the seating face of which the facingpart is superposed, also showing in broken lines the outline of thesuperposed facing part with raised areas of this shown in broken lineshading; and

FIG. d is a graph showing flow characteristics.

The vaporizer includes a body casing 1 closed at its lower end andfurnished with a removable top closure plate 2 which is furnished with agas inlet 3 and a gas mixture outlet 4. For the sake of convenience theinlet 3 and outlet 4 are shown as extending radially in FIG. 1, buttheir true directions are offset from the radial as shown in FIG. 3. Apair of cylindrical wicks 5, 6 dip into anesthetic within the casing andare arranged in the casing in spaced relationship to form an annularpassage 7 for the upflow of gas vapor from the liquid anesthetic 8 inthe base of the casing. This uprising vapor enters an annular groove 9from which a passage 10 leads through the top plate 2. This passage 10(FIG. 3) opens into the seating face of the top plate to register withan almost completely annular groove ill in the facing part 12 of thevalve 13. This facing part 12 may if desired be made of some form ofso-called nonstick material such as polytetrafluoroethylene, which maybe loaded with a strength material such as glass fiber. This form ofmaterial may mitigate sticking of the valve on the seating face whichcan be caused by certain constituents such as Thymol, in volatileanesthetic. This groove 11 is of a narrow width from its front end llato an intermediate point 11b and in this part the groove gets steadilydeeper towards such part lllb. The groove then widens for the partIllcwhich is of even depth. The said groove formation may be changed tosuit other volatile anesthetics and may be of constant width, or changemore than once in width. A further recess 14 is formed in the valve partT2 to form a communication between a part 16 from the inlet 3, and adown passage 1611 (FIG. 3). At the entry to port lb the inflowing gas isdivided into two streams, the other stream passing down a passage 15into bypass system including a port 17 controlled by a valve 18 which inturn is operated by a bimetallic strip acting to increase the valveopening with increasing temperature and to reduce the valve opening withdecreasing temperature. This gas stream emerges through a restrictedpassage 20 into a chamber 21 located axially within the body casing 1.There is an outlet 22 from this chamber which joins the vapor outlet 4for gas to flow from said chamber and combine with vapor flowing up thepassage 7 and into the groove 11 in the valve and from there through aport 23 in the plate 2 to the outlet 4. The other down passage 16a fromthe valve facing recess M- leads into annular groove 24 in the top ofthe body casing 1 and this communicates by a series of holes 25 with avery narrow annular passage 26 for gas to flow theredown on to thesurface of the liquid anesthetic h. This narrow passage 26 and theposition and shape of the wall of chamber 21 tends to cause thedownflowing gas to impinge on the surface of the anesthetic liquid andcauses a certain amount of vapor to be picked up by the gas stream sothat the amount of vapor to be picked up further along the gas stream isreduced, as is the thermal load on the wicks 3 and 6. This vapor asbefore stated flows up the annular passage '7 where further vaporizationof anesthetic from the soaked wicks occurs to escape through the outlet4 with gas which flows up from the chamber 21. The restricted annularpassage 26 lies between the wall of the chamber 21 and an annular makeuppiece 27 which is used to combine with the chamber 21 and wicks and 6 toreduce the volume of gas within the body casing 1 for vaporizationpurposes. An escape hole 28 is provided through the valve for gas topass from the recess 14 to the topside of the valve and so balance thepressure on the two surfaces of the valve 131 The aforesaid valve 13 islocated within an annular guide part 29 secured on top of the plate 2and a spring 30 holds the valve facing 12 down on to the seating face ofthe top plate. The valve is rotated from an off position, wherein partsand 16a are closed by valve facing 12, by a knob 31 secured on the stem32 of the valve and this control knob has a tapering annular scale 33which is graduated to requirements. in operation when the knob isrotated gas will be'allowed to flow from the inlet 3 into the recess 14from the inlet 3 down the bypass system into the chamber 21 through thevalve controlled port 17 to pass up to the outlet 4 whilst anotherstream of gas will be passing down the restricted annular passage 26 tocause vaporization for vapor to flow up to the groove 11 in the valvefacing and from thence become combined with the bypass stream of gas.

For control purposes the groove 11 in the valve facing 12 is made widein relation to its depth so that the cross-sectional area of the grooveis small in relation to the skin surface of the groove. For example, atlow percentage settings the groove 11 may be about 0.2 inch wide andabout 0.002 inch deep giving an area of about 0.0004 square inch.

The aforesaid body casing l is provided with a funnellike filler part 34for the entry of liquid anesthetic and this inlet is closed by a headedstopper 35 which surrounds the head of a drain screw 36 which closes thedrainage outlet 37. The stopper 35 is provided with a socket 38 in itshead so that the stopper can be pulled out, inverted on to the head of adrain screw 36 which can then be screwed back for draining liquidanesthetic from the body casing 1 through passageway 39 and out throughthe outlet 37. There is an observation window 40 through the base partof the body casing 1 for observing the level of the liquid 8.

FIG. 4 illustrates graphically how the bypass system, Line A, variesfrom the streamline flow B, the vertical scale indicating pressure dropover the bypass valve 18 in centimeters water gauge and the horizontalscale indicates gas flow in liters per minute. It will be seen that thepressure drop over valve 18 increases as the gas flow increases.

it is usual to assist a patient's breathing by the use of a pumpingdevice but this normally causes a positive and negative pressure in thegas circuit and a vaporizer so pushing a volume of air into and out ofthe vaporization chamber. The air so pushed becomes further enrichedwith anesthetic and so adversely affects the accuracy of control. Thisinvention, by reducing the volume of gas above the liquid 8 asaforesaid, reduces this enrichment effect to a stage where it may bevirtually negligible.

We have previously indicated that the rotary valve 13 when positioned atone extreme of its range of movement causes both passages connectingwith the vaporizing chamber to be closed so that all the gas flowsthrough the bypass system. By choice of an appropriate shape of thecentral recess 14, and by the provision of extra passages if necessary,it is possible for the rotary valve to provide other functions such asclosing the bypass circuit to allow all the gas to flow through thevaporizing chamber, or providing a bleed to atmosphere for excessanesthetic vapor or providing a direct link between the inlet to andoutlet from the vaporizing chamber.

We claim:

1. Vaporizing apparatus for a volatile anesthetic including;

a body forming a container for liquid anesthetic and wherein such liquidcan be vaporized by the inflow of gas;

a bypass chamber for gas located above said container;

a main inlet to, and a main outlet from, said bypass chamber for thethrough flow of gas' a bypass valve controlling the flow of gas into thebypass chamber;

a temperature-responsive element connected to move said bypass valve toincrease the pressure drop over the bypass valve as the temperaturefalls;

a gas inlet to, and a gas-anesthetic outlet from, said container;

gas inlet passage means for connecting said main inlet to said containergas inlet;

gas-anesthetic outlet passage means for connecting said containergas-anesthetic outlet to said main outlet to mix with gas passing fromsaid container;

a rotary plate valve normally closing said gas inlet and gasanestheticoutlet passages;

means on said plate valve for opening said gas inlet passage throughouta set range of angular movement of said plate valve;

part-annular groove means on said plate valve for opening saidgas-anesthetic outlet passage over a further range of angular movementof said plate valve, said groove means having its depth less than itswidth;

presenting a gas-anesthetic flow path along an arch of at least andbeing of inconstant cross-sectional area to vary the flow ofgas-anesthetic intothe main outlet and thus vary the anestheticconcentration delivered from the vaporizer; and

manual operating means for causing rotation of said valve to initiallyallow gas flow into the vaporizer and then to control the anestheticconcentration delivered from the vaporizer.

2. Vaporizing apparatus according to claim 1 wherein said plate valvehas a valving surface in which said groove means is formed, said valvingsurface being comprised by a material having a low coefficient offriction and resistant to volatile anesthetic constituents, and whereinsaid bypass chamber has a removable cover against which said valvingsurface bears.

1. Vaporizing apparatus for a volatile anesthetic including; a body forming a container for liquid anesthetic and wherein such liquid can be vaporized by the inflow of gas; a bypass chamber for gas located above said container; a main inlet to, and a main outlet from, said bypass chamber for the through flow of gas; a bypass valve controlling the flow of gas into the bypass chamber; a temperature-responsive element connected to move said bypass valve to increase the pressure drop over the bypass valve as the temperature falls; a gas inlet to, and a gas-anesthetic outlet from, said container; gas inlet passage means for connecting said main inlet to said container gas inlet; gas-anesthetic outlet passage means for connecting said container gas-anesthetic outlet to said main outlet to mix with gas passing from said container; a rotary plate valve normally closing said gas inlet and gasanesthetic outlet passages; means on said plate valve for opening said gas inlet passage throughout a set range of angular movement of said plate valve; part-annular groove means on said plate valve for opening said gas-anesthetic outlet passage over a further range of angular movement of said plate valve, said groove means having its depth less than its width; presenting a gas-anesthetic flow path along an arch of at least 180* and being of inconstant cross-sectional area to vary the flow of gas-anesthetic into the main outlet and thus vary the anesthetic concentration delivered from the vaporizer; and manual operating means for causing rotation of said valve to initially allow gas flow into the vaporizer and then to control the anesthetic concentration delivered from the vaporizer.
 2. Vaporizing apparatus according to claim 1 wherein said plate valve has a valving surface in which said groove means is formed, said valving surface being comprised by a material having a low coefficient of friction and resistant to volatile anesthetic constituents, and wherein said bypass chamber has a removable cover against which said valving surface bears. 